1. Field of the Invention
The invention relates to a semiconductor device, and more particularly to a semiconductor device provided with a ferroelectric PZT or PLZT film.
2. Description of the Related Art
PZT (Pb-Zr-TiO.sub.3), PLZT (Pb-La-Zn-TiO.sub.3) or the like has a perovskite structure represented by the general formula ABO.sub.3 and shows a hysteresis effect on an external electric field and a very high dielectric constant. Such materials are actively utilized as a capacitor dielectric film for semiconductor devices such as large-scale DRAMs and non-volatile memory devices.
A principal portion of a conventional non-volatile, memory device having a PZT film is exemplified with reference to FIG. 2(c) as attached herein.
In FIG. 2, 1 is a substrate made of silicon and having thereon an oxide film 2 of SiO.sub.2. A platinum thin film is layered on the SiO.sub.2 film 2, forming an electrode 7 on which a PZT film 6 is deposited.
A preparing method of the semiconductor device as above is as follows.
Silicon halide or hydride is hydrolyzed or oxidized or organic oxysilane is thermally decomposed to form the SiO.sub.2 film on the silicon substrate 1 and platinum is then deposited 1000 to 2000.ANG. on the SiO.sub.2 film 2 by a DC magnetron sputtering method using a platinum target to form the electrode 7 (FIG. 2(a)).
PZT is deposited 2000 to 3000.ANG. in thickness on the electrode 7 by a RF sputtering method using a plasma ion of Ar/O.sub.2 preferably with a sintered PZT target of Ti, Zr and Pb in the ratio of 0.5:0.5:1.15 under reduced pressure to form the PZT film 4 (FIG. 2(b)).
The silicon substrate 1 having thereon the SiO.sub.2 film 2, electrode 7 and PZT film 4 is annealed for 30 mins to 1 hr at 550.degree. to 650.degree.C. in an oxidative atmosphere and then further applied with a separate electrode material in a desired pattern to complete a semiconductor device (not shown).
The semiconductor device uses platinum as the basic electrode 7 and the substrate is annealed after the PZT film 4 is formed on the basic electrode 7. Hence, the annealing causes PbO in the PZT film 4 to readily change to a vapor, leading to that the resultant PZT film 6 lacks Pb, particularly, at an interface between the electrode 7 and the PZT film 6. As a result, there is a problem that the PZT film 6 when provided with a space-charge region at the interface between the electrode 7 and the PZT film 6 is poor in reliability or other properties.